Ionospheric Fading Loss Model

Select the Use checkbox on the Iono Fading tab of the RF Environment properties page to have the Systems Tool Kit^® (STK^®) software invoke this model. The computation for propagation loss through the ionospheric layer is based on the ITU-R P.531-13 recommendation. The total electron content (TEC) along the propagation path causes polarization rotation due to Faraday rotation. The STK software estimates TEC by using the International Reference Ionosphere (IRI) model and integrating electron density over the actual path through the ionospheric layer.

The STK application uses section 3.2 of the ITU-R P.531-13 recommendation to compute the Faraday rotation and the cross-polarization discrimination for aligned antennas to estimate the potential loss. The cross-discrimination loss is interpreted as the fading loss in the link budget. You should use the model based on the system polarization type. For example, circular polarization is expected to experience little impact, while linear polarization systems may be very sensitive to small rotations. Also, smaller wavelengths may see more phase changes (and higher loss) from minor position changes. The STK application leaves it up to you to be aware of the sensitivity of the results to the environmental factors (TEC) and the platform dynamics and to apply good judgment in using the model.

The reference data used by the IRI model is an integral part of the model, and the IRI conference regularly issues updates to the data. STK processing computations use the Space Weather access point (AP) data file. Using the 2016 version (updated for September 2019 changes) of the IRI model, STK processing computes the TEC and ionospheric noise temperature.

AGI routinely updates apf107.data and ig_rz.dat (magnetic data). However, for a given release, the installed data has a limited time span of applicability. You should make sure your analysis stays within the limits of these files. If your analysis goes outside the limits, the STK Message Viewer will display a message indicating that data is not available for the scenario date. To help avoid this situation and to have the best data available, you should periodically update these two data files using the STK Data Update Utility, which is under the Utility menu. This pulls the latest data files from the AGI data server or from your organization's server that is bringing in data from the AGI server. If no servers are directly available, see the section "Updating data without an internet connection" in the Data Update Utility help topic page. Please contact support@agi.com if you need assistance.

Alternate AP data

The following parameters provide an option to use an alternate file for AP data (not for magnetic data).

Because you can update files through the Data Update Utility, AGI recommends that you avoid using this option.

Parameter	Description
UseAlternateAPFile	Select this check box to override the built-in AP dataset.
AlternateAPDataFile	Click the ellipsis to find and select a user-supplied file. This file will override the apf107.dat file provided by the IRI model. This file must be in exactly the correct format, otherwise the STK application will not be able to continue processing your scenario.